Measurement of $CP$ asymmetries in $B^0 \to K_S^0 \pi^0 \gamma$ decays at Belle II

Abstract We report measurements of time-dependent $CP$ asymmetries in $B^0 \to K^0_S π^0 γ$ decays based on a data sample of $(388\pm6)\times10^6$$B\bar{B}$ events collected at the $Υ(4S)$ resonance with the Belle II detector. The Belle II experiment operates at the SuperKEKB asymmetric-energy $e^+e^-$ collider. We measure decay-time distributions to determine $CP$-violating parameters $S$ and $C$. We determine these parameters for two ranges of $K^0_S π^0$ invariant mass: $m(K^0_S π^0)\in (0.8, 1.0)$$GeV/c^2$, which is dominated by $B^0 \to K^{*0} (\to K^0_S π^0) γ$ decays, and a complementary region $m(K^0_S π^0)\in (0.6, 0.8)\cup(1.0, 1.8)$$GeV/c^2$. Our results have improved precision as compared to previous measurements and are consistent with theory predictions.
Tags
Working group Time Dependent CP Violation
Principal authors @  Koji Hara, Akimasa Ishikawa, Kenkichi Miyabayashi, Kazutaka Sumisawa, Yuma Uematsu, Yutaka Ushiroda
Reference Phys.Rev.Lett. 134, 011802 (2025), DOI: 10.1103/PhysRevLett.134.011802
Document BELLE2-PUB-PH-2023-010
Links arXiv:2407.09139, Inspire, PRL
Bibtex 
@article{Belle-II:2024uzp,
    author = "Adachi, I. and others",
    collaboration = "Belle-II",
    title = "{Measurement of CP Asymmetries in B0{\textrightarrow}KS0{\ensuremath{\pi}}0{\ensuremath{\gamma}} Decays at Belle II}",
    eprint = "2407.09139",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II Preprint 2024-009, KEK Preprint 2024-1",
    doi = "10.1103/PhysRevLett.134.011802",
    journal = "Phys. Rev. Lett.",
    volume = "134",
    number = "1",
    pages = "011802",
    year = "2025"
}